1. Field of the Invention
The present invention relates to a method for controlling the operation of a variable displacement refrigerant compressor, especially a variable displacement wobble plate type compressor accommodated in a car air-conditioner, and driven by a car engine via a solenoid clutch. More particularly, it relates to a method for controlling the operation of a variable displacement refrigerant compressor accommodated in a car air-conditioner by which an acceleration of a car engine is not adversely affected when starting the car after a temporary stoppage of the car.
2. Description of the Related Art
Generally, a variable displacement refrigerant compressor accommodated in a car air-conditioner is driven by a car engine via a solenoid clutch, and therefore, when the car is to be started or accelerated, a large load due to inertia of the car per se, and an additional load due to the inertia of the variable displacement refrigerant compressor of a car air-conditioner, are simultaneously applied to a car engine, and accordingly, the acceleration of the car engine is adversely affected.
Japanese Unexamined Patent Publication No. 57-195884 discloses one compressor operating method intended to solve such problems of the conventional car air-conditioner. Namely, the method of Japanese Unexamined Patent Publication No. 57-195884 is carried out in a manner such that when an overall load applied to a car engine exceeds a predetermined value, a detection signal is transmitted to a control means to decrease a displacement of a variable displacement compressor. More specifically, to carry out the above-mentioned method, an accelerator pedal of the car is operatively connected to a drive means which drives a displacement changing member of variable displacement refrigerant compressor, and therefore, the displacement changing member of the compressor, e.g., a conventional non-rotary wobble plate of a variable displacement wobble plate type compressor as disclosed in, for example, U.S. Pat. No. 4,428,718 to Skinner, is moved by the drive means between maximum and minimum displacement positions in association with a movement of the accelerator pedal of the car.
Alternatively, an engine speed detector is arranged to detect the number of rotations of a crankshaft of the car engine, and a detected speed signal is transmitted to an electric control device of the air-conditioner. Therefore, when the control device detects that a rate of change in the speed of the car engine is larger than a predetermined value, the above-mentioned drive means for driving the displacement changing member is operated to move the displacement changing member from the maximum to the minimum displacement position.
Nevertheless, in the former case wherein the drive means of the variable displacement refrigerant compressor is operated in association with the movement of the accelerator pedal of the car, the drive means is operated only after the accelerator pedal is pressed down from an initial position to a predetermined position, and therefore, the operation of the drive means involves a time delay ranging from 0.5 second to 1.0 second with respect to the movement of the accelerator of the car, and accordingly, this time delay of the operation of the drive means prevents a rapid acceleration of the car.
In the latter case wherein the drive means of the variable displacement refrigerant compressor is operated in connection with speed of the car engine, the time needed for the detection of the engine speed carried out by the engine speed detector, as well as for the calculation of the rate of change in the detected engine speed carried out by a differential circuit means of the electric control device of the compressor, is substantial, and therefore, the operation of the drive means to move the displacement changing member of the compressor is delayed, and accordingly, a rapid acceleration of the car is prevented as in the former case.
At this stage, when a car provided with an air-conditioner is driven in the city, the car must repeatedly stop, start, and accelerate from a temporary stoppage at many intersections. During a temporary stoppage of the car, the car engine is idling at a low rotation speed, and as a result, the compressor of the air-conditioner is necessarily rotated at a low speed at which the compressing motion of the compressor is slow. Therefore, the displacement changing member of the compressor is often forcibly moved to the maximum displacement position to increase the refrigerating function of the air-conditioner, and thus, when the car is to be started and accelerated from a temporary stoppage, a relatively long time is needed to move the displacement changing member of the compressor back to minimum displacement position. Particularly, when a variable displacement wobble plate type compressor is accommodated in the air-conditioner, the position of the displacement changing member consisting of a wobble plate is determined by a dynamic relationship among pressures in a crankcase chamber, a discharge chamber, a suction chamber of the compressor, and a force of return spring arranged to urge the wobble plate toward the minimum displacement position, and consequently, it generally takes 3 to 6 seconds for the displacement changing member to be moved to the minimum displacement position. Therefore, the car engine cannot be rapidly accelerated due to a load of the variable displacement refrigerant compressor.